1. Field of the Invention
The present invention relates to a clutch mechanism used in an image forming apparatus, such as a printer, a facsimile, a copier, etc., and an image forming apparatus equipped with the same.
2. Description of the Related Art
In recent years, cost reduction, downsizing, and power saving are attempted in various systems, such as an image forming apparatus (e.g., a copier and a printer), etc. For example, a reduced number of driving sources (e.g., a motor or the like) is disposed in a narrow space with a planetary gear mechanism that decelerates an rpm (revolutions per minute) thereof as described in Japanese Patent Application Publication No. 2009-73648 (JP-2009-73648-A).
Specifically, to downsize the system a driving force transmission mechanism (e.g., a reverse driving unit) functioning as both a planetary gear deceleration mechanism and a planetary gear clutch mechanism (i.e., a planetary clutch mechanism) is employed to switch between forward and reverse rotations. The driving force transmission mechanism includes two planetary gear clutch mechanisms respectively placed upstream and downstream in a driving force transmission direction. Each planetary gear clutch mechanism includes an inner teeth gear at a driving force input site, a planetary gear that meshes with the inner teeth gear, a sun gear that meshes with the planetary gear, and a holder that holds the planetary gear.
Accordingly, torque transmitted to the inner teeth gear is outputted through the holder by bringing the sun gear into a rotation prohibited state. An external teeth gear is also coaxially integrally provided on an outer circumferential surface of the inner teeth gear while an external teeth gear is integrally provided on a periphery of the holder coaxially with the inner teeth gear in each planetary gear clutch mechanism. The external teeth gear integral with the inner teeth gear provided on the upstream side meshes with a driving gear (i.e., a driving force input gear). The external teeth gear integral with the inner teeth gear provided on the downstream side meshes with the external teeth gear on the upstream side via an idler gear. The respective external teeth gears integral with the holders of the upstream and downstream sides directly mesh with each other. The external teeth gear of the downstream side meshes with a driving force output gear that transmits the torque to a driving unit provided downstream.
A projection as a rotation prohibiting target (i.e., a rotation prohibited section) is integrally formed on the sun gear in each of the planetary gear clutch mechanisms not to rotate the sun gear when the rotation prohibiting target is prohibited from rotating. A projection (i.e., a rotation prohibiting device) serving as a rotation prohibiting member is also provided. When these projections engage each other, the sun gear is prohibited from rotating thereby entering a fixed state.
The projection of the rotation prohibiting member of each planetary gear clutch mechanism has an L-shape obtained by applying a bending process to a tip of a plate like member (hereinafter referred to as an L-shaped projection), and both sides of the projection engaging the rotation prohibiting target are parallel with each other. The side of the L-shaped projection becomes substantially parallel to a straight line extended through a rotational center of the rotation prohibiting target when it engages one side of the projection of the rotation prohibiting target.
One side of the projection of the rotation prohibiting target is formed almost parallel to each side of the L-shaped projection when engaging one side of the L-shaped projection. By contrast, the other side of the projection of the rotation prohibiting target has a slope inclining from the one side of the L-shaped projection when engaging the L-shaped projection during its rotation to smoothly guide the L-shaped projection. Since the side of the rotation prohibiting target and the side of the L-shaped projection are parallel to each other, these sides can engage on a plane, and accordingly an engagement state is rarely cancelled maintaining a fixed state of the sun gear even if any shock occurs during the engagement. However, since the rotation prohibiting target itself rotates, impact sound and/or free vibration of the rotation prohibiting member unavoidably occur when the rotation prohibiting member engages the L-shaped projection. Accordingly, there is a need for development of a clutch mechanism and an image forming apparatus with the clutch mechanism capable of reducing such noise while suppressing the free vibration and the impact.